The present invention relates to a method for making contact lens hydrophilic. More particularly the invention relates to a method for imparting good wettability by water to hard contact lens which is normally poor in surface wettability by water. 2. Description of Prior Art
In the conventional hard contact lenses, the materials comprising polymethyl methacrylate as main component have been used because of their excellent optical properties, high physical strength and good machinability. Recently, importance has been recognized on the supply of oxygen through contact lens for the metabolism of cornea, and the polymers containing silicon or fluorine have come to be used popularly as lens material because of their excellent oxygen permeability. Typical examples of such silicon-containing polymers are silicon rubber and the polymers of acrylates or methacrylates having siloxane bond in the side chain.
The polymers of acrylates or methacrylates having a perfluoroalkyl group in the side chain can be cited as typical examples of fluorine-containing polymers.
These materials, although having excellent oxygen permeability, are poor in surface hydrophilicity, and many of them show a strong water repellancy. The contact lens with poor surface hydrophilicity, i.e., poor wettability with tear liquid has the problem that it could make improper correction of eyesight. It also has the problem of unfitness or giving a sense of disagreeableness to the wearer because of unsmooth movement of the lens on the horny coat of the eye.
Various proposals have been made for providing good surface hydrophilicity to such lens materials. For instance, Japanese Patent Publication No. 56-39450 and Japanese Patent Application Laid-Open (Kokai) No. 58-7418 and 59-19918 disclose the methods for improving hydrophilicity of lens materials by means of copolymerization with hydrophilic monomers.
Also, Japanese Patent Publication No. 57-35443 and Japanese Patent Application Laid-Open (Kokai) No. 58-17412 disclose the methods for forming lens materials by using a polymerization component having a functional group that can be after-treated for imparting hydrophilicity to the contact lens surface by an after-treatment.
Further, Japanese Patent Publication No. 55-49288 and Japanese Patent Application Laid-Open (Kokai) No. 58-216222 disclose the methods for making hydrophilic the surface of contact lens made of a silicone resin by plasma treatment or plasma polymerization.
Said methods comprising copolymerization with hydrophilic monomers, however, have the defect that because of the contradictory tendency of the proportion of hydrophilic monomer in composition and the oxygen permeability of contact lens, an attempt to impart sufficient hydrophilicity to the lens surface may cause excessive lowering of oxygen permeability while an attempt to maintain high oxygen permeability may result in poor hydrophilicity of the lens surface. Generally, the silicon- or fluorine-containing monomers used as oxygen permeability imparting component have the problem that when they are copolymerized with hydrophilic monomes, the resulting polymers tend to become cloudy because of strong hydrophobicity.
Also, in the case of the methods in which contact lens is formed by using a compound having a specific functional group as polymerization component for the purpose of making the lens surface hydrophilic by an after-treatment, there are the problems that the materials which can be made hydrophilic are limited to a specific type and that oxygen permeability of the material is lowered as in the case of copolymerization with hydrophilic monomers.
The method for making the contact lens surface hydrophilic by plasma treatment is impractical since the effect of making the lens surface hydrophilic tends to die away in a short time and also such effect may be lost by various causes such as drying of the lens which may take place in ordinary use of the lens. Recently, grafting of hydrophilic monomers to the contact lens surface by plasma polymerization is tried, but this technique is defective in durability of water wettability and also tends to give rise to the same problems as in the case of said plasma treatment. Further, setting of the treating conditions is very complex and delicate in the methods comprising said plasma treatment or plasma polymerization. The effect of treatment is greatly affected not only by such fundamental parameters as power for plasma treatment, treating time, degree of vacuum, etc., but also by such factors as configuration of the apparatus and retained state or position of the lens. Thus, the lenses treated according to these methods are poor in durability and repeatability.
Still further, the apparatus used for said plasma treatment or plasma polymerization necessitates specific equipments such as vacuum system and high-frequency power source. This coupled with said complex setting of treating conditions makes the operations complicate and troublesome to carry out.
Accordingly, an object of this invention is to provide a method for making the contact lens surface hydrophilic, by which the contact lens is provided with the ability to effect proper correction of eyesight and good fitness to the eye without being impaired in its inherent properties such as oxygen permeability, optical characteristics and mechanical strength.
Another object of the present invention is to provide said method for making the contact lens surface hydrophilic, which method is easy to practice, can realize long-time retension of effect of the treatment and can provide the lens with good durability and repeatability.
Other objects and advantages of the present invention will be apparent from the following description of the invention.